摘要
A collimated light beam will be refracted if it propagates through a flow-field with index-of-refraction variations,and its wavefront will be distorted.If we measure the deflection angle of the light beam,the gradient of the wavefront can be obtained using the Malus law,and the wavefront aberration can be computed with a reconstruction algorithm.Two characteristics of background oriented schlieren(BOS) are conducive to wavefront aberration measurement:BOS can be used to measure the deflection angle of a light beam by measuring the displacement field between the reference image and the experiment image.Moreover,in a BOS system of Schlieren mode,only the ray perpendicular to the background image can be captured with a camera.This is helpful to measure wavefront aberrations that occur after a planar wavefront has passed through the flow-field.Based on these characteristics of BOS of Schlieren mode,a new wavefront measurement technique,which is called the BOS-based wavefront technique(BOS-WT),is proposed in this paper.It works by constructing the relationship between the displacement of the background image and the aero-optical wavefront gradient and uses the Southwell wavefront reconstruction algorithm.A BOS-WT system was assembled,and its temporal resolution was found to be 6 ns,and its temporal-correlation resolution reached 0.2 μs.A BOS-WT can measure the time-correlation transient wavefront quantitatively.It is simple and easy to operate.In this paper,we also present a study of the aero-optical performance of supersonic mixing layer based on our BOS-WT transient wavefronts at an interval of 5 μs.The results showed the wavefront was transient and distorted after it had passed through the mixing layer.Through the analysis of the data at the 5 μs interval,the temporal evolution of wavefront can be obtained.
A collimated light beam will be refracted if it propagates through a flow-field with index-of-refraction variations, and its wavefront will be distorted. If we measure the deflection angle of the light beam, the gradient of the wavefront can be obtained using the Malus law, and the wavefront aberration can be computed with a reconstruction algorithm. Two characteristics of background oriented schlieren （BOS） are conducive to wavefront aberration measurement： BOS can be used to measure the deflection angle of a light beam by measuring the displacement field between the reference image and the experiment image. Moreover, in a BOS system of Schlieren mode, only the ray perpendicular to the background image can be captured with a camera. This is helpful to measure wavefront aberrations that occur after a planar wavefront has passed through the flow-field. Based on these characteristics of BOS of Schlieren mode, a new wavefront measurement technique, which is called the BOS-based wavefront technique （BOS-WT）, is proposed in this paper. It works by constructing the relationship between the displacement of the background image and the aero-optical wavefront gradient and uses the Southwell wavefront reconstruction algorithm. A BOS-WT system was as- sembled, and its temporal resolution was found to be 6 ns, and its temporal-correlation resolution reached 0.2 ~ts. A BOS-WT can measure the time-correlation transient wavefront quantitatively. It is simple and easy to operate. In this paper, we also present a study of the aero-optical performance of supersonic mixing layer based on our BOS-WT transient wavefronts at an interval of 5 μs. The results showed the wavefront was transient and distorted after it had passed through the mixing layer. Through the analysis of the data at the 5 μs interval, the temporal evolution of wavefront can be obtained.
